Contributions of spontaneous polarization (P
s) to capacitance (C) in ferroelectric liquid crystal (FLC) cells are analyzed in the present paper. Reorientation properties of FLC molecules have been studied on the basis of capacitance vs applied voltage characteristics. In the course of polarization reversal, C increases as the component of P
s parallel to the substrate of the cell becomes large.
A method for molecular alignment of a ferroelectric smectic liquid crystal is reported. Homeotropic alignment with a small angle of pretilt was obtained by surface treatment with oblique deposition of metal oxide, such as yttria and alumina. Furthermore, an electric field was applied during the cooling period from isotropic liquid to chiral smectic phase. Uniformly pretilted alignment could be obtained by using the oblique deposition and DC field application. On the other hand, a twisted alignment was obtained on the obliquely deposited metal oxide film when an AC electric field was applied instead of a DC field. Electrooptical characteristics of these cells are shown.
There are still problems not fully solved concerning the characteristics and magnitude of interaction between liquid crystals and the surfaces of substrates. It is thought that the number of electrodes in a matrix display device can be increased and its display panel can contain a memory function by the weak boundary‐coupling effect (i.e., by reducing the coupling of the liquid crystal and the substrate surface). Thus, it is necessary to investigate the strength of the coupling between liquid crystals and the surfaces of various substrates. The coupling strength is measured by curve fitting of the electrostatic capacitance–applied voltage characteristic (the C ‐ V characteristic) of a nematic liquid crystal cell. In this method the measured result of the C ‐ V characteristic is compared with the result of calculation in which the surface coupling coefficient is used as parameter. Two kinds of surface treatment (i.e., oblique vacuum‐evaporation of silicon monoxide and rubbing after coating with polyvinyl alcohol film) are investigated. The nematic liquid crystals used in this study are phenyl cyclohexane‐based. The coupling coefficient is of the order of 10−3 J/m2. When the temperature is raised, the coupling coefficient decreases.
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